“I broke my arm on this movie doing a stunt,” Eckhart tells PopcornBiz. “I was doing a stunt and I jumped off a seven foot thing and landed and broke my arm and kept on going. I did the whole last half of the movie with a broken arm, which I thought was fun!”

For Eckhart, making the alien invasion film – shot in hyper-realistic documentary style – was the ultimate grownup version of playground war games. “I was like a kid in a candy store,” he says. “There were days when we shot 20,000 rounds in a day. I remember going through this, and we shot this movie in Louisiana and I remember being up at 3 a.m. in Shreveport on top of a humvee with a .50 cal, going through the streets. Now, to you that might not seem like fun, but to me it was blast.”

“We shut down freeways for the movie, we shut down a whole overpass that was riddled with over turned tanks, crashed helicopters, all this sort of stuff, for hundreds of yards,” he remembers. “I thought, 'If anybody was coming into Shreveport that night to just stay for a day and go to a business meeting or whatever they would've thought that this town was at war,' and I loved that. “

Cast Aside: Actors Who Almost Had the Part

Eckhart was sold on the project early on – enough to shoot a test sequence to aid director Jonathan Liebsman’s bid to land the film’s helming duties. “Jonathan showed me a page on YouTube.com and that was some Marines going house to house, going through them in Fallujah, and it was both organized yet chaotic,” he explains. “It was unpredictable – these guys were showing their training and they showed their youth. And Jonathan said this is what the movie is going to look like and right then I said 'I'm in. I'll die for this part.’”

Along with tackling an intense USMC-style training regimen long before shooting started, Eckhart also joined a cadre of 40 Marines in the mountains of Afghanistan to better understand their war zone bonds. The actor says it was important to him to “get to know the Marines: the hierarchy, the mentality, the psychology. And then we went through a boot camp. We did three weeks in the middle of Louisiana. It was hotter than hell and we lived in a tent.”

“It was interesting how far some actors would go and how much they would buy into it and believe it because when you're out there and I'm yelling at you in character and the actor is like, 'Dude, I'm just an actor!' It was a good way for us to erase our real lives and get into character, which helped immensely in the movie.”

Underneath the Hollywood-style slam-bang action, Eckhart says, “we mean to honor the Marines and the soldiers. What they had to do is obviously much more serious and intense than what we did, but we felt like we honored them pretty realistically the best we could."

“I think this is going to be a ‘hoo-rah’ moment for them.”

Published at 1:07 PM PST on Mar 10, 2011 | Updated at 11:46 AM PDT on May 30, 2012